src/json/encode.lua

   1 --[[
   2         Licensed according to the included 'LICENSE' document
   3         Author: Thomas Harning Jr <harningt@gmail.com>
   4 ]]
   5 local externalIsArray = IsArray -- Support for the special IsArray external function...
   6
   7 local tostring, string, type = tostring, string, type
   8 local tonumber, math, assert = tonumber, math, assert
   9 local table, pairs, ipairs = table, pairs, ipairs
  10 local getmetatable, setmetatable = getmetatable, setmetatable
  11 local select = select
  12 local print = print
  13 local error = error
  14 local null = require("json.util").null
  15
  16 module("json.encode")
  17
  18 local encodingMap = {
  19         ['\\'] = '\\\\',
  20         ['"'] = '\\"',
  21         ['\n'] = '\\n',
  22         ['\t'] = '\\t',
  23         ['\b'] = '\\b',
  24         ['\f'] = '\\f',
  25         ['\r'] = '\\r',
  26         ['/'] = '\\/'
  27 }
  28
  29 -- Pre-encode the control characters to speed up encoding...
  30 -- NOTE: UTF-8 may not work out right w/ JavaScript
  31 -- JavaScript uses 2 bytes after a \u... yet UTF-8 is a
  32 -- byte-stream encoding, not pairs of bytes (it does encode
  33 -- some letters > 1 byte, but base case is 1)
  34 for i = 1, 255 do
  35         local c = string.char(i)
  36         if c:match('%c') and not encodingMap[c] then
  37                 encodingMap[c] = string.format('\\u%.4X', i)
  38         end
  39 end
  40 local function encodeString(s)
  41         return '"' .. string.gsub(s, '[\\"/%c%z]', encodingMap) .. '"'
  42 end
  43
  44 local function isArray(val)
  45         if externalIsArray and externalIsArray(val) then
  46                 return true
  47         end
  48         -- Use the 'n' element if it's a number
  49         if type(val.n) == 'number' and math.floor(val.n) == val.n and val.n >= 1 then
  50                 return true
  51         end
  52         local len = #val
  53         for k,v in pairs(val) do
  54                 if type(k) == 'number' and select(2, math.modf(k)) == 0 and 1<=k then
  55                         assert(isEncodable(v), "Invalid array element type:" .. type(v))
  56                         if k > len then -- Use Lua's length as absolute determiner
  57                                 return false
  58                         end
  59                 else -- Not an integral key...
  60                         return false
  61                 end
  62         end
  63
  64         return true
  65 end
  66
  67 local function tonull(val)
  68         if val == null then
  69                 return 'null'
  70         end
  71 end
  72
  73 -- Forward reference for encodeValue function
  74 local encodeValue
  75 local alreadyEncoded -- Table set at the beginning of every
  76         -- encoding operation to empty to detect recursiveness
  77 local function encodeTable(tab)
  78         if alreadyEncoded[tab] then
  79                 error("Recursive table detected")
  80         end
  81         alreadyEncoded[tab] = true
  82         local retVal = {}
  83         -- Try for array
  84         if isArray(tab) then
  85                 for i = 1,(tab.n or #tab) do
  86                         retVal[#retVal + 1] = encodeValue(tab[i])
  87                 end
  88                 return '[' .. table.concat(retVal, ',') .. ']'
  89         else
  90                 -- Is table
  91                 for i, v in pairs(tab) do
  92                         local ti = type(i)
  93                         if ti == 'string' or ti == 'number' or ti == 'boolean' then
  94                                 i = encodeString(tostring(i))
  95                         else
  96                                 error("Invalid object index type: " .. ti)
  97                         end
  98                         retVal[#retVal + 1] = i .. ':' .. encodeValue(v)
  99                 end
 100                 return '{' .. table.concat(retVal, ',') .. '}'
 101         end
 102 end
 103
 104 local function encodeNumber(number)
 105         local str = tostring(number)
 106         if str == "nan" then return "NaN" end
 107         if str == "inf" then return "Infinity" end
 108         if str == "-inf" then return "-Infinity" end
 109         return str
 110 end
 111
 112 local allowAllNumbers = true
 113
 114 local encodeMapping = {
 115         ['table'  ] = encodeTable,
 116         ['number' ] = allowAllNumbers and encodeNumber or tostring,
 117         ['boolean'] = tostring,
 118         ['function'] = tonull,
 119         ['string' ] = encodeString,
 120         ['nil'] = function() return 'null' end -- For the case that nils are encountered count them as nulls
 121 }
 122 function isEncodable(item)
 123         return encodeMapping[type(item)] and not (type(item) == 'function' and item ~= null)
 124 end
 125
 126 --[[local ]] function encodeValue(item)
 127         local encoder = encodeMapping[type(item)]
 128         if not encoder then
 129                 error("Invalid item to encode: " .. type(item))
 130         end
 131         return encoder(item)
 132 end
 133
 134 function encode(data)
 135         alreadyEncoded = {}
 136         return encodeValue(data)
 137 end
 138
 139 local mt = getmetatable(_M) or {}
 140 mt.__call = function(self, ...)
 141         return encode(...)
 142 end
 143 setmetatable(_M, mt)